I plan to do a pc upgrade very soon. Alongside that I plan to start with Mint or Fedora. Is there any real or big downsides to dual booting ? Aside from the harddrive space lost ?
If I like or really like my time with Mint I would probably switch permanently but I felt like I wanted to test it for a couple of months before making a complete switch.
Im a big 
so that impacts my consideration. Dont really play much multiplayer shooters so I dont have a problem with kernel anticheat games not working.
There’s a lot of concern in the replies about the bootloader and an ntfs dmz.
It’s easy to recover from a messed up bootloader, the last step of your installer usb usually has an automated system for installing a bootloader, try that and see if it works and that’s your fix.
Ntfs is not a problem. It has not been a problem for decades. Make sure your windows has quick boot turned off (this is the setting that uses “hibernate” technology in place of an actual “boot” in order to come up faster. It sets a flag saying so in an ntfs partitions description that makes the iirc fuse driver freak the fuck out). This step is a precursor to being able to resize that partition, so it’s necessary if you don’t go the more complex two disks route. You can also stop using the ntfs driver in linux that has this problem.